Housings for automotive electrical components have been made to provide a function (an internal pressure regulating function) of preventing the housing breakage due to the rise of the internal pressure by eliminating the differential pressure between the interior and the exterior of the housing. A ventilation member using a porous membrane is known as a ventilation member giving such a function to the housing. For example, ventilation members (it is called “air permeable plug” in JP 2003-063549 A) disclosed in JP 2003-063549 A, JP 2004-358746 A, and JP 2004-249653 A include a cylindrical main body as a support body and include a porous membrane bonded to the main body by insert molding.
Generally, the capability of the above-mentioned ventilation member to eliminate the differential pressure is depending on the gas permeability of the porous membrane and the size of the porous membrane. Therefore, in order to enhance the capability to eliminate the differential pressure, one may enlarge the area of the porous membrane or may improve the gas permeability of the porous membrane.
However, the gas permeability of the porous membrane already has reached a level in which it is difficult to find room for improvement. On the other hand, the enlargement of the area of the porous membrane cannot be adopted easily because it deteriorates the dust/water-proof performance of the ventilation member. In recent years, restrictions on the size of the ventilation member have become severe with the miniaturization of the housing that should have the internal pressure regulating function.
The insert molding disclosed in JP 2003-063549 A can improve the bonding strength between the porous membrane and the main body. In insert molding, as shown in FIG. 11, a porous membrane 103 is positioned and fixed to a molding die 101 with check pins 102, and then resin is injected to a cavity KV. Therefore, it is difficult to obtain a gas-permeable area larger than the opening area of the main body. Moreover, the portion of the porous membrane 103 between the pins 102 and 102 is crushed because of the pressure of the pins 102, resulting in the loss of the gas-permeation function. As a result, the gas-permeable area in some cases becomes smaller than the opening area of the main body.